[ruby-core:69569] [Ruby trunk - Feature #11158] Introduce a Symbol.count API as a more efficient alternative to Symbol.all_symbols.size

Issue #11158 has been updated by Marc-Andre Lafortune.


Franck Verrot wrote:
> I'm not sure to fully understand why we make `Symbol` extend `Enumerable` rather than returning a new enumerator object

It's not "rather than". `Symbol.each` without a block will return an `Enumerator`, that we extend `Enumerable` or not.

> Isn't there way to much overhead to include `Enumerable` in `Symbol`?

Not sure what you mean by overhead. There's no performance cost to it. It adds a bunch of methods to `Symbol`, and many won't be helpful (I doubt someone would use `Symbol.map{...}`, but I 'm not sure I see the downside.


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Feature #11158: Introduce a Symbol.count API as a more efficient alternative to Symbol.all_symbols.size
https://bugs.ruby-lang.org/issues/11158#change-52906

* Author: Lourens Naud辿
* Status: Open
* Priority: Normal
* Assignee: Koichi Sasada
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We're in the process of migrating a very large Rails codebase from a Ruby 2.1.6 runtime to Ruby 2.2.2 and as part of this migration process would like to keep track of Symbol counts and Symbol GC efficiency in our metrics system. Preferably still while on 2.1 (however this implies a backport to 2.1 as well), but would definitely be useful in 2.2 as well.

Currently the recommended and only reliable way to get to the Symbol counts is via Symbol.all_symbols.size, which:

* Allocates an Array
* rb_ary_push and walking the symbol table isn't exactly efficient

Here's some benchmarks:

~~~
./miniruby -Ilib -rbenchmark -e "p Benchmark.measure { 10_000.times{ Symbol.count } }"
#<Benchmark::Tms:0x007f8bc208bdd0 @label="", @real=0.0011274919961579144, @cstime=0.0, @cutime=0.0, @stime=0.0, @utime=0.01, @total=0.01>
~~~

~~~
./miniruby -Ilib -rbenchmark -e "p Benchmark.measure { 10_000.times{ Symbol.all_symbols.size } }"
#<Benchmark::Tms:0x007fa47205a550 @label="", @real=0.3135859479953069, @cstime=0.0, @cutime=0.0, @stime=0.03, @utime=0.29, @total=0.31999999999999995>
~~~

I implemented and attached a patch for a simple Symbol.count API that just returns a numeric version of the symbol table size, without having to do any iteration.

Please let me know if this is inline with an expected core API, anything I could clean up further and if there's any possibility of such a change also being backported to 2.1 as well? (happy to create a new patch for 2.1)

---Files--------------------------------
symbol_count.patch (4.4 KB)
symbol_enumerator.patch (6.07 KB)


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